What are the functions of all the parts of a computer?

Different Computers are assembled differently, so it varies somewhat from one computer to another. I will give you the basic parts of a standard desktop computer:
The Case - It holds everything inside it. I seriously hope you already knew about this one.
The Central Processing Unit (CPU) - This term is often erroneously used to refer to a computer tower. It is the primary chip that performs most of the computing tasks of a the computer. Major manufacturers are Intel and AMD. It is the primary determiner of a computer’s performance.
The Motherboard - A large printed printed circuit board that connects all the parts together. Most of the computer’s ports are located on the motherboard. It also holds some lesser chips such as the Chipset (which is actually one chip. It used to be multiple chips, but on modern platforms the functions of these chips have been either moved directly onto the CPU, or onto one chip which is surface mounted to the motherboard.) It holds a socket for the CPU, slots for RAM, as well as various other connectors for expansion, including PCIe, USB and SATA. It also holds the CPU voltage regulation module as well as other power delivery circuitry. Features and exact expansion and ports vary from one model to another. It is the primary determiner of features on the computer.
CPU Cooler - This is usually a heatsink with a fan
on it, however it can also sometimes be a
watercooling system. Its role is to dissipate heat
from the CPU into the air.
Random Access Memory (RAM) - This is where
data relating to what you are currently doing is
stored. It is a very fast-access type of memory, but
it is volatile, meaning that it is not for long term
storage, and loses all the data it holds when
powered off. RAM is made in chips, but each chip
holds very little. In desktops and laptops, there are
multiple chips that are surface mounted to a PCB
that is inserted into RAM slots on the motherboard.
In laptops, it is sometimes surface mounted directly
to the motherboard.
The Graphics Card or Video Card - This is different
from a GPU. The GPU (Graphics Processing Unit) is
the chip that handles graphics processing in a
particular computer. The GPU is surface mounted to
the Graphics Card, but the graphics card also has
power delivery circuitry, cooling, and video output
ports.
The Power Supply - The name is self-explanatory.
It supplies power to the different components in a
computer. It is usually internal, but sometimes can
be an external brick, in which case the
motherboard contains additional power delivery
circuitry.
Wireless Network Card - Allow the computer to
connect to Wi-Fi.
Storage Drives - Several types exist. Many
computers have multiple storage drives:
Solid State Drives - an internal device that stores
data long-term. It uses NAND flash memory to
store data that can be accessed quickly. It is much
faster and somewhat more reliable than a hard
disk drive, but are much more expensive for the
same capacity. (1 TB HDD about 50 USD, 1 TB SSD
often over 250 USD) They are usually used as
primary boot drives (C:) because of their speed.
However, they are often cost-prohibitive to use as
the only storage drive in a computer. They are
usually 2.5-inch drives connected to the
motherboard by SATA, or PCBs inserted into a slot
on the motherboard (M.2 or mSATA)
Hard Disk Drives - Slow, long-term data storage.
They are inexpensive, so usually used as a
secondary drive to store large amounts of data that
does not need to be accessed quickly.
Keyboard, Mouse, Microphone, Camera - usually
external devices that allow input to the computer
Screen, Speakers - I seriously hope you know
what these do.
Keep in mind that many other parts exist that are
sometimes present, and that parts vary from one
computer to another. This is in no way an exhaustive
list, but a list of the primary components.

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